Continuous settled density analyses



I Sept. 22, 1970 H. 1... ERSKINE ETAL 3,53@,Mfi

CONTINUOUS SETTLED DENSITY ANALYSES Filed Feb. 1, '1968 BITUMINOUS DILUENT TAR'SANDS 36 CENTRIFUGE zoNE 'ITDMEN WATER AND STEAM I 2 C COMBINED I PRODUCT FROTH SEW' SETTLED SCAVENGER /FROTH 4 PRIMARY SCREEN FROTH FROTH l SETTLER |3- 32 sCAvENCE-R 34 FROTH 7 sE PARATloN I5 ZONE T AIR OIL-RICH t M|[)D| |NG3 FLOTATION SCAVENGER 2 I4 '7 33 v ZONE SAND 25 o L-LEAN TA|| |NG5 MIDDLINGS 1 SEPARATED MIDDLINGS CENTRlF-UGAL? DENSITY 4 SEPARATION 5' GAGE zoNE CoNsTANT'v VOLUME PUMP BOTOMS INVENTOR.

United States Patent Canada Filed Feb. 1, 1968, Ser. No. 702,394 Int. Cl. Cg 1/00 U.S. Cl. 196-1452 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a system and method for continuously controlling the hot water process for the treatment of tar sands. The improvement in the process comprises introducing a portion of process separation zone middlings into a centrifugal separation zone, continuously separating mineral material which will not pass a 325 mesh screen from the middlings in the centrifuge zone to continuously provide a separated middlings to a hereinafter specified measuring zone, continuously introducing the separated middlings into the measuring zone, continuously measuring the density of the separated middlings and continuously regulating the Water entering and leaving the process separation zone in response to the measurements so as to continuously control the viscosity of the middlings in the zone. The system used for continuously controlling the viscosity of the middlings comprises a centrifugal separator, a density sensing device, and regulating means responsively connected to the sensing device to control the water withdrawn from the separation zone.

This application relates to an improvement to the hot Water process for separating bitumen from tar sands. Specifically this application relates to an improvement to the inventions disclosed and claimed in United States applications Floyd et al., Ser. No. 509,589 and now US. Pat. No. 3,401,110 issued Sept. 10, 1968 and Graybill et al., Ser. No. 684,292.

This invention relates to a system and method for continuously controlling the hot water process for the treatment of tar sands. Large deposits of these sands are found as the Athabasca deposits in northern Alberta, Canada. The evaluated portion of these deposits occupies about five and one-half million acres and is buried by Zone to 2000 feet of overburden. It has been estimated that these deposits consist of about 600 billion barrels of reserves in place, more than 350 billion barrels of recoverable reserves of raw tar sand oil and more than 250 billion barrels of upgraded synthetic crude oil.

The tar sands are primarily composed of a fine quartz sand having a particle size greater than that passing a 325 mesh screen. The quartz sand is impregnated with a viscous bitumen in quantities of from 5 to 21 weight percent of the total composition. More typically the bitumen content is from 8 to percent. This bitumen is quite viscous and conains typically 4.5 percent sulfur and 38 percent aromatics. Its specific gravity at 60 F. ranges typically from about 1.00 to about 1.06. In addition to the bitumen and quartz sand, the tar sands contain clay and silt in quantities of from 1 to weight percent of the total composition. Silt is normally defined as material which will pass a 326 mesh screen but which is larger than 2 microns. Clay is material smaller than 2 microns including some siliceous material of that size.

Several basic extraction methods have been known for many years for the separation of bitumen from the sands. In the so-called cold water method, the separation is accomplished by mixing the sands with a solvent ca pable of dissolving the bitumen constituent. The mixture is then introduced into a large volume of water, water with a surface agent added, or a solution of a neutral salt in water. The combined mass is then subjected to a pressure or gravity separation.

In the hot water method, the bituminous sands are jetted with steam and mulled with a minor amount of hot water at temperatures in the range of to 210 F. The resulting pulp is dropped into a stream of circulating hot water and carried to a separation cell maintained at a temperature of about to 200 F. In the separation cell, sand settles to the bottom as tailings and bitumen rises to the top in the form of an oil froth. An aqueous middlings layer containing some mineral and bitumen is formed between these layers. A scavenger step may be conducted on the middlings layer from the primary separation step to recover additional amounts of bitumen therefrom. This step typically comprises aerating the middlings as taught by K. A. Clark, The Hot Water Washing Method, Canadian Oil and Gas Industries 3, 46 (1950). These froths can be combined, diluted with naphtha and centrifuged to remove more Water and residual mineral. The naphtha is then distilled off and the bitumen is coked to a high quality crude suitable for further processing.

The present invention relates to a system and process for controlling the operation of the hot water process set out in Floyd et al., US. patent application Ser. No.

509,589 and now US. Pat. No. 3,401,110 issued Sept. 10, p

1968 and is also an improvement to the system and process disclosed in Graybill et al., US. patent application Ser. No. 684,292. Floyd et al. teach a hot water process for recovering additional bitumen in which the water incorporated with the bituminous sands for discharge into the separation cell and the rate of passage of the middlings from the separation cell to the scavenger step are both regulated in order to maintain the density of the middlings layer within the range of 1.03 to 1.50 and/or the viscosity of the middlings within the range of 0.56 to 10 centipoises.

Graybill et al. teach that the viscosity of the middlings should be maintained within the range of about 0.4 to about 5.7 centipoises measured at F. 'with typical operation at about 1 to 2 centipoises at 190 F. As Floyd et al. point out, the viscosity is relatable to middlings clay content which can be maintained by regulating the amount of water incorporated with the bituminous sands in an initial pulp forming stage and the rate of passage of the middlings from the separation cell to the scavenger step. Graybill et a1. disclose that middlings clay content is relatable to the settled density of the middlings where settled density is defined as measured density determined when mineral material which will not pass a 325 mesh screen has substantially settled out from the middlings sample. The viscosity of the middlings in the separation cell can be maintained within. the desired range of about 0.4 to 5 .7 centipoises by regulating the clay content of the middlings by maintaining the settled density of the middlings within the range of about 1.03 to 1.09 g./ml.

The process of Graybill et a1. comprises introducing a portion of the middlings from a hot water process separation cell into a sampling system. In the sampling system, entrained sand is substantially removed by settling [from the portion of the sample which is to be analyzed. The density of the sample is measured when the sample has settled and the water incorporated into the tar sands and the stream to the scavenger zone from the separation cell are regulated in response to the measurement so as to maintain the viscosity of the middlings in the separation cell within the range of 0.4 and 5.7 centipoises or preferably about 1 to 2 centipoises. The portion of the middlings on which the measurements are run is typically comprised of about 1 to weight percent bitumen and 20 to 35 weight percent total mineral of which about 1 to 3 percent is clay. The density of the dragstream settled is typically between about 1.05 and 1.07 g./ml. at 190 F.

The Graybill et al. invention provides a means for intermittently measuring settled density and controlling viscosity of the middlings. The settled density measurements are made batchwise and provide an intermittent electrical signal representing density. As such this signal is not best .suited for automatic control purposes. A memory unit can be provided in the Graybill invention as part of the density sensing means to hold the signal from one batch measurement on over to the next measurement to provide a smooth constant control.

The present invention provides a system and process for continuously measuring the settled density of the middlings and continuously controlling the middlings viscosity without a memory unit. One of the problems in providing a continuous control for measuring middlings viscosity is that the middlings direct from the separation cell contain material which will not pass a 325 mesh screen. For an accurate and consistently standard determination of middlings density this material must be removed. The system of Graybill et al. accomplishes this by settling in a sample cell. This, of course, removes the material but necessitates a batch-wise operation and an intermittent control. The present invention advantageously provides a system and process for continuously measuring settled density of middlings and continuously controlling the middlings viscosity. The advantage of the present invention is provided by passing a continuously removed portion from the separation cell to a centrifugal separation zone which provides a continuous sample to the density sensing device. The process of the present invention is describable as an improvement to the hot water process for separating bitument from tar sands where the hot water process comprises forming a mixture of water and bituminous tar sands, passing the mixture to a process separation zone to form an upper bitumen froth layer, a lower sand tailings layer and a middlings layer comprising water, mineral and bitumen, and separately removing the froth layer, sand tailings layer and middlings layer from the process separation zone. The improvement is describable as comprising introducing a portion of the middlings into a centrifugal separation zone, continuously separating minerial material which will not pass a 325 mesh screen from the middlings to continuously provide a separated middlings, continuously introducing the separated middlings into a measuring zone, continuously measuring the density of the separated middlings in the measuring zone and continuously regulating the water entering and leaving the hot water process separation zone in response to the measurements so as to continuously control the viscosity of the middlings in the zone.

'In this specification the term separated density is defined as measured density of separated middlings and the term separated middlings is defined as middlings which has been subjected to a centrifugal separator step to substantially remove mineral material which will not pass a 325 mesh screen. Separated density measurements will be substantially the same as settled density measurements, the latter determined by the apparatus and system of the Graybill et a1. invention.

The process of this inveniton may be best described with reference to the drawing. The figure is a preferred embodiment of the invention and shows a flow sheet of the hot water process utilizing the improved continuous middlings control system of the present invention.

In the drawing, bituminous tar sands are fed into the system through line 1 where they first pass to a conditioning drum or muller 3. Water and steam are introduced from 2 and mixed with the sands. The total water so introduced is a minor amount based on the weight of the tar sands processed and generally is. in the range of to 45 percent by weight of the mulled mixture. Enough 4 steam is introduced to raise the temperature in the conditioning drum to within the range of to 210 F. and preferably to above F.

An alkali metal-containing alkaline reagent can also be added to the conditioning drum usually in amount of from 0.1 to 3.0 pounds per ton of tar sand. The amount of such alkaline reagent preferably is regulated to maintain the pH of the middlings layer in the separator zone within the range of 7.5 to 9.0. Best results seem to be obtained at a pH value of 8.0 to 8.5. The amount of the alkaline reagent that needs to be added to maintain a pH value in the range of 7.5 to 9.0 may vary from time to time as the composition of the tar sands as obtained from the mine site varies. The best alkaline reagents to use for this purpose are caustic soda, sodium carbonate or sodium silicate, although any of the other alkali metalcontaining alkaline reagents can be used if desired.

Mulling of the tar sands produces a pulp which then passes from the conditioning drum as indicated by line 4 to a screen indicated at 5. The purpose of screen 5 is to remove from the tar sand pulp any debris, rocks or oversized lumps as indicated generally at 6. The pulp then passes from screen 5 as indicated by 7 to a sump 8 where it is diluted with additional water from 9 and a middlings recycle stream 10. This recycle stream serves to provide sufficient liquid to make the tar sands pulp pumpable so that it can be transferred to the separator.

As a general rule the total amount of water added to the natural bituminous sands as liquid water and as steam prior to the separation step should be in the range of 0.2 to 3.0 tons per ton of the bituminous sands. The amount of water needed within this range increases as the silt and clay content of the bituminous sands increases. For example, when 15 percent by weight of the mineral matter of the tar sands has a particle size below 44 microns, the fresh water added generally can be about 0.3 to 0.5 ton per ton of tar sands. On the other hand, when 30 percent of the mineral matter is below 44 microns diameter, generally 0.7 to 10 tons of water should be used per ton of tar sands.

With further reference to FIG. 1, the pulped and diluted tar sands are pumped from the sump 8 through line 11 into the separation cell 12. The cell contains a relatively quiescent body of hot water which allows for the formation of a bitumen froth which rises to the cell top and is withdrawn via line 13, and a sand tailings which settles to the bottom to be withdrawn through line 14. An aqueous middlings layer between the froth and tailings layer contains silt and clay and some bitumen which failed to form froth. Since sufiicient clay is not removed in the sand tailings withdrawn from the bottom of the separation cell through line 14 in order to prevent the buildup of clay in the system it is necessary to continually remove some of the middlings layer and supply enough water in the conditioning operations to compensate for that so removed. The rate at which the middlings need to be removed from the system depends upon the content of clay and silt present in the tar sands feed and this will vary from time to time as the content of these fines varies. If the clay and silt content is allowed to build up in the system, the viscosity of the middlings layer will increase. Concurrently with such increases an increase in the proportions of both the bitumen and the sand retained by the middlings will occur. If the clay and silt content is allowed to build up too high in the system, effective separation no longer will occur and the process will become inoperative. This is avoided by regulating the recycling and withdrawal of middlings and input of fresh water per the present invention. Even when the separation step is operating properly the middlings layer withdrawn through line 15 will contain a substantial amount of bitumen which did not separate. Hence the middlings layer withdrawn through line 15 is, for purpose of description, herein referred to as oil-rich or bitumen-rich middlings.

The amount of bitumen removed in the oil-rich middlings layer is related to the percentage of clay and/or silt present in the tar sands being processed, varying directly with the amount of clay and/ or silt present. For example, typical bitumen recovery values for primary froth from tar sands in which percent of the mineral matter is less than 44 microns and from sands in which 25 to 30 percent is less than this size are respectively 85 percent and 60 percent. For commercial operation it is highly desirable to obtain increased froth yield in the separation zone over such values as those which are obtainable heretofore by the hot water process. This is particularly true when the tar sands as mined contained a relatively high proportion of clay and silt components.

The bitumen-rich middlings stream withdrawn from the separator 12 through line 15 is sent to a scavenger zone 16 wherein an air flotation operation is conducted to cause the formation of additional bitumen froth. A stream of the middlings is withdrawn from the separation cell '12 and is conducted via line 17 by constant volume pump 18 to the centrifugal separation zone 19. The centrifuge or cyclone in separation zone 19 separates the stream of middlings (typical density 1.15) into an overhead stream 20 (typical density 1.05 to 1.06) and a bottoms stream 21 (typical density 1.5 to 1.6). The overhead stream 20, which is separated middlings, passes to the density gauge 22 where separated density is continuously measured to control variable speed pump 23 on line 15. The separated middlings are discharged from the density gauge via line 24.

Any liquid cyclone or centrifugal separator can be used for the centrifugal separation step. A representative ma chine of this type is a solid bowl centrifuge which consists of a truncated cone fixed to and rotating at high speed in a horizontal shaft. An internal spiral rotates at a slightly slower speed to continuously remove solids deposited on the inner surface of the cone or bowl. Feed enters the cone by means of the hollow center shaft while overflow passes from the cone or bowl through ports at the small end of the cone.

Another suitable separator is a liquid-solid cyclone. In this apparatus feed furnished by a pump enters tangentially into the upper section of the liquid cyclone at suflicient pressure to support the vortex action of the middlings in the unit. The centrifugal forces in the vortex throw the coarse mineral to the walls of the cylone where they collect and pass downward and out of the unit through the bottom orifice. The middlings move to the inner spiral of the vortex and are displaced upward to the outflow.

The density sensing device 22 is preferably a radiation density gauge but again other density sensing devices can be used here. Referring again to the drawing, the density gauge controls variable speed pump 23 via control line 25 so that if the separated density rises above the range 1.03 to 1.09, lead 25 increases the variable speed pump 23 thereby increasing the flow in line 15 to the scavenger cell 16. Increased flow to the scavenger cell 16 lowers the interface level between the middlings and froth in the separation cell 12. The lowering of the interface level actuates float valve 26 which by means of lead 27 opens valve 28 thus increasing the flow of fresh water addition to the sump 8 via 9. Increased water flow through line 9 results in increased water content in the diluted pulp passing from the sump 8 through line 11 to the separation cell 12. Flow through valve 29 is decreased via lead 30 which responds to the increase in water in the diluted pulp thereby resulting in a reduction in the amount of middlings recycle diluting the separation cell feed via 10. Thereby the proportion of fresh water in the separation cell 12 is increased, bringing about a decrease in middlings density. Correspondingly, if the settled density of the separated middlings decreases below the operation range of 1.03 to 1.09, lead 25 decreases the variable speed pump 23 thereby decreasing the flow in line 15 to the scavenger cell 16. Decreased flow to the scavenger cell raises the interface level in the separation cell 12. A raising of the interface level actuates float valve 26 which by means of lead 27 closes valve 28 thus decreasing the flow of fresh water addition to the sump via line 9. Decreased water flow through line 9 results in decreased water content in the diluted pulp passing from the sump 8 through line 11 to the separation cell 12. Flow through valve 29 is increased via lead 30 which responds to the decrease in water in the diluted pulp in 11 thereby resulting in an increase in the amount of middlings recycle diluting the separation cell feed. Thus the proportion of fresh water in the separation cell 12 is decreased bringing about an increase in middings density. The system can be operated so as to maintain the middlings density within the preferred range of 1.05 to 1.07 instead of the broad range as described supra.

Following the process further, in the scavenger zone 16 an air flotation is conducted by any of the air flotation procedures conventionally utilized in processing of ores. This involves providing a controlled zone of aeration in the flotation cell at a locus where agitation of the middlings is being effected so that air becomes dispersed in the middlings in the form of small bubbles. The drawing illustrates a flotation cell of the sub-aeration type wherein a motorized rotary agitator is provided and air is fed thereto in controlled amounts. Alternatively the air can be sucked in through the shaft of the rotor. The rotor effects dispersion of the air in the middlings. This air causes the formation of additional bitumen froth which passes from the scavenger zone 16 through line 31 to a froth settler zone 32. An oil-lean middlings stream is removed and discarded from the bottom of the scavenger zone via line 33.

In the settler zone 32 the scavenger froth forms into a lower layer of settler tailings which is withdrawn and recycled via line 34 to be mixed with bitumen-rich middlings for feed to the scavenger zone 16 via line 15. In the settler zone 32 an upper layer of upgraded bitumen froth forms above the tailings and is withdrawn through line 35 and mixed with primary froth from line 13 for further processing.

The combined froths are at a temperature of about F. They are heated with steam and diluted with suflicient naphtha or other diluent from 36 to reduce the viscosity of the bitumen for centrifuging in zone 37 to produce a bitumen product 38 suitable for further processing.

What is claimed is:

1. In a system for conducting a hot water process for treating tar sands comprising a conditioning drum; a separation cell; a first line for supplying tar sands pulp from said conditioning drum to said separation cell; a second line for introducing hot water into tar sands pulp in said first line; a third line for withdrawing a bitumen froth product from said cell; a fourth line for withdrawing a sand tailings layer. from said cell; a fifth line for withdrawing a middlings portion from said cell; a sixth line for recycling a middlings portion from said cell to be mixed with said tar sand pulp prior to discharge into said cell; the improvement which comprises:

(a) a centrifugal separator for receiving middlings from said cell and for continuously separating mineral which will not pass a 325 mesh screen from said middlings to provide a separated middlings;

(b) a density sensing device connected with said centrifugal separator for measuring the settled density of said separated middlings;

(c) regulating means controllably attached to said fifth line, and responsively connected to said density sensing device to control the middlings portion withdrawn via said fifth line in response to said settled density measurement of separated middlings;

(d) regulating means operating in response to said middlings withdrawn in said fifth line and connected to said second line to control the hot water introduced to the bituminous tar sands pulp via said second line; and

(e) regulating means operating in response to said hot water incorporated in said second line and connected to said sixth line to control the middlings portion recycled to the bituminous tar sands pulp via said second line.

2. The system of claim 1 in which said density sensing device (b) comprises a radiation density detector comprising a radiation source, a radiation measuring means positioned with respect to the said source to measure radiation from said source and an amplifier, indicator and recorder unit connected to said measuring means to translate radiation measurements to electrical energy which actuates said regulating means (c) and (d).

3. The system of claim 1 in which said regulating means (c) is responsively connected to said density sensing device so as to increase the viscosity of said middlings in said separation cell when said middlings viscosity is below 0.4 contipoise and so as to decrease the viscosity of said middlings in said separation cell when said middlings viscosity is above 5.7 centipoises.

4. The system of claim 1 in which said regulating means (0) is responsively connected to said density sensing device so as to increase the viscosity of said middlings in said separation cell when said separated middlings density is below 1.03 g./ml. and so as to decrease the viscosity of said middlings in said separation cell when said separated middlings density is above 1.09 g./ ml.

References Cited UNITED STATES PATENTS 'DELBERT E. GANTZ, Primary Examiner T. H. YOUNG, Assistant Examiner US. Cl. X.R. 

